There is a known HUD apparatus that is mounted to a mobile body and displays a virtual image of an image so that an occupant can visually confirm the image. The HUD apparatus disclosed in Patent Literature 1 includes an optical source part, which has a light emission element emitting an optical source light, a condenser lens, which faces the optical source part and collects an optical source light, and a field lens, which further collects the optical source light from the condenser lens side and projects the optical source light at a predetermined angle. The HUD apparatus further includes an image formation element, which forms an image by the optical source light entering from the field lens side and emits the light of the image to a projection member side.
The field lens forms a single surface made of a single optical surface, as a surface on the condenser lens side and as a surface on the image formation element side. A diffusion plate is arranged between the condenser lens and the field lens, as a diffusion part that diffuses an optical source light.